1. Field of the Invention
The present invention pertains to attitude reference systems, and more particularly to an attitude reference system which is used to guide an escape vehicle such as an aircraft ejection seat. In a broader sense, however, the present invention could be used on any kind of vehicle or object where determining orientation relative to the earth is important or desirable.
1. Description of the Prior Art
Prior attitude sensing systems for use on aircraft ejection seats have used mechanical adjustments to align the rocket thrust axis with the center of mass of the crewmember/seat pair. This alignment is necessary to prevent excessive rotation rate of the crewmember/seat after ejection, but it does not guide the seat. Other systems employ drogue parachutes to prevent tumbling and to stabilize the crewmember/seat until the velocity has been reduced to a value where crewmember/seat separation and main parachute deployment may safely proceed.
Guided seats thus far have been described which use electrostatic sensing as a means to distinguish different orientations in space. U.S. Pat. No. 3,979,089 to Miller et al. presents one electrostatic system. Such systems, however, may behave unpredictably if an inversion in the earth's electric field occurs as near a thunderstorm. An attitude reference system can be constructed using inertial subsystems; however, inertial components require long ready times, frequent maintenance, and may depend on vulnerable aircraft systems.
Unguided seats offer little protection to pilots during inverted or high sink rate ejections near the earth's surface. Many fatalities if such out of envelope ejections occur, even though the seat functions as it is intended to function.